DIY CO2 Probe Information, For What It Is Worth

[Biollante]

Hi,

I have had a couple of email requests for information on my do-it-yourself CO[SUB]2[/SUB] probe experience.

Notice I went out and bought a CO[SUB]2[/SUB] meter, so I cannot claim great diy success.

First off, my interest and most of my original information came from Vaughn of Hoppy fame. I also got a lot of information from various internet posts and I cannot find the other primary resource that as I recall was a Russian language source.

My membrane trials were based on or natural offshoots of a couple of lists posted by Tom Barr as “Plantbrain” elsewhere.

I had noticed my “test tube” drop checkers had quicker response time, so Hoppy’s observation made sense.

So, based on Hoppy’s observation that high surface area to reference solution volume I first tried setting up drop checkers based on surface area to reference solution volume.

• Low and behold, Hoppy was correct.:surprise:

The simplest form being like this DIY Co2 Meter where it is easy to vary surface area to reference solution volume and since the reference solution does not have to be read, the volume of reference solution only need to be sufficient to cover the probe element.

For pH probes, I had a Hanna pH meter, a diy pH probe and a Milwaukee meter.

It appears that most LDPE (low-density polyethylene), LLDPE (Linear low-density polyethylene ) is even better work so all kinds of sandwich wraps and bags work films work to one degree or another, the "Saran Wrap" style being the worst, almost unusable, to thinner, true LLDPE wraps working reasonably well, obviously the thinner the better.

I cannot locate the DO membrane from Hach I tried; I think they were something like Standard DO membrane kit for DO probe 05521-00, I found these too fragile for a complete lummox as I to handle.

Parafilm is another I have not tried, but have heard good reports, in fact I lost the reference but it seems quite successful.

It appears gsjimia references an interesting product in the thread “CO2 tester using PH probe,” post #2. That is likely better than anything I tried.

Of the things I tried, the best all round, is a product called Tyvek, readily available from home improvement stores and in various types of clothing and in mailers, as in the lined priority mail, mailers. The stuff is tough, keeps water out and gas, CO[SUB]2[/SUB] anyway move through quickly. :beguiled:

As always these things depend on high surface area to reference solution volume and the accuracy of the 4-dKH, or whatever reference solution chosen.

In making a reference solution with baking soda, I think it is worth drying it out even in the dry area I live I can see a difference. There is some bogus information out on the internet regarding drying baking soda.

Never let the temperature exceed 70⁰C (158⁰F), somewhere around 70-80⁰C baking soda loses CO[SUB]2[/SUB], of course this is why we like it for baking, but it is bad form for our purposes. So, we must gently force the excess moisture out of the baking soda without turning it into Sodium carbonate.

• Place twice as much baking soda as you think you need, on a nonreactive surface, I like parchment paper on a cookie sheet.
• Most ovens in the US, I am familiar with start at 150⁰F (65.6⁰C) that is the temperature I use.
• Leave for 2-hours
• Weigh the amount you require, return the excess to its container.

Making the largest the initial quantity of solution the greater the likely accuracy of the reference solution. While I know 50-liter, solutions are a bit much…

• A little less than 5-grams (4.989-g) of baking soda, then add enough distilled water to make 5-liters (~4.995-l).

OR

• A little less than 2.5-grams (2.494-g) of baking soda, then add enough distilled water to make 2.5-liters (~2.498-l).

OR

• A little less than 1-gram (0.998-g) of baking soda, then add enough distilled water to make 1-liter (~0.999-l).

All three solutions result in 40-dKH.

For the 4-dKH reference solution

• mix 1 part 40-dKH solution with 9 parts distilled water
  • Mix 10-ml 40-dKH solution with 90-ml of distilled water, for example.

Biollante

 

[gsjmia]

Mr. B, I spent a good deal of time reading about this topic and appreciate your post.

But, assuming that a "Co2 probe" were reasonably successful and accurate-will it yield any useful diagnostics? In other words, is it worth the trouble?

It seems to me it will shed at least some (a hopefully a lot) light on this frustrating Co2 issue. I don't want to spend 10 years learning Co2.

Over and over Tom keeps beating the Co2 drum and many seem not to hear-maybe because its a lot easier to tweak EI or add more light and as Tom says "Co2 is hard".

 

[Tom Barr]

The higher the surface area, the more you lose accuracy within a narrow area. Say you want to measure the CO2 around a small leaf........if the area is 10x larger than the leaf, then you lose some of the accuracy, it integrates and takes an average. As long as this area is small, this is okay.

If you reduce the distance and the membrane diffusion coefficient, this this will increase Flux measurement.
Area will do this also, but reduction in the gap will also.

As far as baking soda, just use sodium carbonate instead.

It's what many use in place of baking soda for alkalinity reference solutions.
Also, the larger the volume of the reference solution, the more accurate it will be.
Much easier to be precise with 10,000mls vs 10 mls for +/- 0.1ml or 10,000mg vs 10 mg's.

Since your measuring errors will be reduced relative to the volume/mass etc.......of the total solution made(eg, the % error will go way down).

 

[Tom Barr]

Mr. B, I spent a good deal of time reading about this topic and appreciate your post.

But, assuming that a "Co2 probe" were reasonably successful and accurate-will it yield any useful diagnostics? In other words, is it worth the trouble?

This is one of the best questions yet.

I'm not so sure it will/does.

But.........and here's the hook............we can at least measure it and demonstrate the range of effective CO2, assuming that the methods are relative standard and the a good CO2 reference calibrates the CO2 probe(which given hobbyists love of short cuts......will cause issues).
This will likely show a much wider range and likely a higher ppm value than what many like to suggest is "plenty of CO2! I know it cannot possibly be a CO2 issue!!".

The other informative thing is that we can data log easily with a pH meter and convert this to data log CO2 over the 24 hour time period.

This shows what your CO2 concentration is doing in the tank/in situ.
You can also see if the CO2 is impacted if you say.........do a noon time burst with 2x more light. There should be a decline if things are running good etc.
If you raise the lights up, more CO2 ppm should be present, increase, less and so on...........using a data logger can show this pretty easily actually.

It seems to me it will shed at least some (a hopefully a lot) light on this frustrating Co2 issue. I don't want to spend 10 years learning Co2.

Over and over Tom keeps beating the Co2 drum and many seem not to hear-maybe because its a lot easier to tweak EI or add more light and as Tom says "Co2 is hard".

I'm not sure there is an easy way to learn CO2.

Watch the plants, fish and use good high grade stuff, set up a good wet/dry filter, have adjustable light, good current etc.
Do it slow and progressive and watch carefully when adjustments are made.
A device will help you make management decisions, but it will not manage them for you
Those assumptions are yours.

 

[Biollante]

That My Friend is the $64,000 Question

Hi,

Given the high price of CO[SUB]2[/SUB] meters and probes, I suspect for most reasonable purposes the do it yourself probes, seem a reasonable alternative.

I think the demand for 4-second response time is a tad unrealistic, but I suspect that with the type of material you have ordered you should easily get under 10-seconds, with little bounce. Part of the response time involves the pH meter and probe.

I think you can do better than a bag around the probe. It rather depends on the shape of your probe, but from what I could tell it seemed an advantage to have some structure around the probe. I think one of the better designs I had based on a 15-ml graduated box sample container from, a Tetra DO test kit, never thought much of the test kit, but I sure liked the sample container.

• By cutting out the wide opposing side, leaving structure at the top,
• wrapping the Tyvek around the container
  • sealed the top where the probe went in with plumbers’ putty.
• The container provided structure and the
• Tyvek was strong enough it protected the reference solution and probe this worked well with my Hanna pH meter and my diy pH probe.

With the Hanna, the response time got into the 20-25 second range, a little bouncing but not bad. I might have been able to do better, certainly I could have worked for a structure that would allow less reference solution, remember maximize surface area, minimize solution.

For many tight areas I have found with good sampling technique you can use the probe as a bench test device.

Let me back up a bit.
The odd thing is CO[SUB]2[/SUB] meters are in my ever-humble-potted-plant- opinion useless when adjusting operational CO[SUB]2[/SUB] levels in aquariums. As with much of the test equipment, they may help understand what worked or tracking over time.

• From an operational point of view, our senses and tuning ourselves to the plants, critters, sights, smells and feel are far more relevant.

I came to my real interest in CO[SUB]2[/SUB] levels from studying circulation issues; I had been sticking test tube drop checkers all over, six to 12 checkers in each of six tanks, placing them based on flow I was tracking principally by dropping different weights of plastic and differing concentrations of Potassium permanganate around the tank.

I wasn’t as smart as Wet to come up with using different values for reference solutions to nail the CO[SUB]2(aq)[/SUB] with some precision.

• Had Wet been around instead of that clown Czado, who knows I may have never purchased a CO[SUB]2[/SUB] meter?

Once it occurred to me that, the alkalinity in our aquariums is about 99% bicarbonate the use of a pH meter made sense, from there it was an easy step to the diy probe, the results were perplexing and on I went to proper CO[SUB]2[/SUB] meters with ion specific probes.

The better the equipment got, the more confused I became, I got mainly catcalls here and demands I get things calibrated, it did not change the results and I notice as more people get the equipment they get the same results, though for some reason no demand everything be calibrated, suddenly, factory calibration and reference solutions are enough.:surprise:

Biollante

 

[Tom Barr]

The alkalinity is some aquariums is 99% bicarb, others? No way...........I've measured many places across the country with well over 100ppm up to 220-300ppm ranges...........and the fish where just fine.........plants doing well etc.
Non carbonate alkalinity is a real issue for using the pH/KH chart.
For some, not hardly any issue however.

Depends on the tap water itself and what they need to add to stabilize pH/alkalinity. Many treatment plant operators lament the issues with maintaining a pH or alkalinity.
A known reference solution for CO2 to compare and check your response/settling times and accuracy is also critical.

I see little issues with a sealed flash with a pH/CO2 probe holder and known volume of DI/KH reference solution water(or better yet, the tank water itself degassed) and a known weight of frozen CO2 dry ice.
A large container holding 1 liter and say 100mg of dry ice in cold conditions.and moved quickly from the scale to the water and sealed rapidly should not affect things too greatly.

I think this is a much better way than using 12 gram paint ball cartridges and unloading those into a flask.
You cannot vary the paint ball amount and the pressure will crack some folk's stuff trying to do this. It will not end well for many.


Factory calibrations are not enough.

I questioned them and questioned them at Oxyguard. Not satisfied, I developed my own methods using pH/Kh reference solutions and a pH meter, then measured that with the Oxyguard............
Next, for a zero CO2 calibration, I bubbled N2 gas into a sealed flask for 30 min.

Since the pH/KH reference is adjusted by CO2 gas, I can vary the ppm.

With the Dry ice method, I have set points, say 5ppm, 20ppm and 50ppm and 100ppm.
Dry ice is cheap.

2 of the Oxyguard probes where sent back.
1 was accurate though.

You are only as good as your method and no one is above skepticism.

 

[Biollante]

Pretty Much You & Hoppy Set The Terms

Hi Tom,

Yes, I should have been clear; bicarbonate is about 99% of the alkalinity in my water,

• I suspect that it is for most tap water at least based on the sampling of water reports, granted not comprehensive, of folks in this forum.
• Also granted that in some of those water reports there is not enough information to be conclusive.
  
• Based on my (granted, limited) observations ammonia/ammonium (rotting material? High DOC?) appear to be the bigger interferences.
  
• But I accept your rebuke.

Fully agree with reference samples being important.

The specific reference to surface area to volume was based on

1. speed of stable reading an issue you and Hoppy introduced at the time.
2. An important reason mentioned was mobility,
   1. the reason I cared about, mention and tested for structural integrity.

I never claimed that reducing the amount of reference solution increased accuracy or precision,

• the thing that amazed me was that they were as accurate as they were.
• As I recall the accuracy, comparison was with drop checkers.

I suggested baking soda as opposed to washing soda, due to the availability and that among us poor schmuck hobbyists it is the reference available.

I cannot think of a single original thing I have come up with here, primarily I try things other folks say, many times it is months or even years before I can draw a conclusion and I end up applying to another situation. Early on you derided me for it, I still do not understand why you or anyone should object to repeatability.

My interest in testing the membranes was for usability and reasonable (for a hobbyist) accuracy.

As demonstrated the placing the pH probe into an oversized drop checker gave improved accuracy (compared to drop checkers), but took 30-minutes to an hour to stabilize and had a great deal of lag in reporting change.

As I think, I mentioned these probes are not going to compete with even the cheapest CO[SUB]2[/SUB] probe and meter on the market.

I do not ever recall thinking using paintball cartridges to create a reference solution, though sparging is a recognized method.

I also agree dry ice is wonderful, I use a lot of it.

Calibration certification is expensive and for the hobbyist purposes uncalled for, I am never going to deal with a sample that requires me to be within 2-parts per billion. A reasonable reference standard with the emphasis on repeatability is in my ever humble-potted-plant opinion far more important than precision instrumentation.

Across the board, I tend to think the obsession with numbers in parts per whatever, borders on the ridiculous.

Never really asked anyone not to be skeptical, in fact, I guess what has troubled me most is that when looking for help with methodology or in figuring out which way to go with something, little more than derision. It is okay I have the means to hire whatever help I need.

It doesn’t matter either another person can do it or not. I work hard to keep the language understandable and it will be easier shortly for me to post the methodology and my nifty collection of calibration certificates.

A nice person offered me some materials to work with, I appreciate the confidence in me, but I think the more people trying things and reporting the results the better. But no one should be offended that those of us lacking formal education is these should use precisely the language and parameters you and your acolytes set forth.

I think this stuff is fascinating, I have no fear of changing my view based on evidence, and I do so all the time, part of what I love about this site.

In some areas, I have entirely changed my views from what they were two years ago and honestly, I hope that is the case two years from now.

There is no need for straw dog arguments.

Biollante